This application relates to wireless communications.
Wireless communication systems can include a network of one or more base stations to communicate with mobile station (MS) such as a wireless device, a mobile device, cell phone, or wireless air card. A mobile station can be referred to as a user equipment (UE) or subscriber station (SS). In some implementations, a wireless communication system covers a certain geographic area by dividing the area into radio cells, each cell can include one or more sectors. A base station can provide wireless coverage in a radio cell. Further, a wireless communication system can include a core network to control the base stations.
A base station can transmit a signal on a forward link (FL), called a downlink signal, to one or more mobile stations. A mobile station can transmit a signal on a reverse link (RL), called an uplink signal, to one or more base stations. Types of wireless communication techniques used by base stations and mobile stations include Frequency Division Duplex (FDD) and Time Division Duplex (TDD).
Wireless FDD systems support downlink and uplink transmissions on different frequency channels. For example, the FL and RL are assigned to different frequency channels with little or no interference between the channels. Therefore, a BS can transmit signals to mobile stations on the FL independently while a mobile station sends signals to a serving BS on the RL.
Wireless TDD systems support downlink and uplink transmissions on the same carrier frequency in separate non-overlapping time intervals. For example, the FL and RL are assigned to the same frequency channel. A wireless communication system can allocate downlink and uplink intervals to control downlink and uplink transmissions in one or more frames. When switching between downlink and uplink transmissions, TDD systems can use a guard period (GP) as a buffer between different transmissions. Wireless systems can use a frame structure to control downlink and uplink transmissions and guard periods. A frame structure can specify locations or intervals within a frame for downlink and uplink transmissions and guard periods.
In some implementations, a frame can include multiple FL slots and RL slots. In some implementations, a frame can include multiple PHY frames for data transmissions. A BS can transmit signals to MSs on FL slots while MSs are scheduled to receive signals in the FL slots. Likewise, a MS can transmit signals to a BS on RL slots while the BS is scheduled to receive signals in the RL slots. FL slots and RL slots can alternate in the time domain and can repeat every frame to allow both the BS and the MSs an opportunity to transmit and receive signals.
A wireless TDD system can combine a TDD technique with a multiple access technology such as Code Division Multiple Access (CDMA) or Orthogonal Frequency-Division Multiplexing (OFDM). Examples of wireless TDD systems include wireless communications networks based on 3GPP2 Radio Transmission Technologies (RTT), Ultra Mobile Broadband (UMB) TDD, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA), Long Term Evolution (LTE) TDD mode, and IEEE 802.16 WiMAX TDD mode.